I recently put together a 10.5" 9mm AR, and it shot incredibly well. A couple of days before my first match with this short fun gun, I pulled it apart to lube it up. Evidently, and unbeknownst to me, the firing pin spring took off when I pulled the bolt to lube it up. When I reassembled it, I put everything back together...except I had never had a blowback AR apart before so I didn't know there was supposed to be a spring on the firing pin. I didn't test fire the gun before the match, and stage 1 turned into a cluster. Oh the value of a $2 spring! When I figured out what was wrong, it was a quick fix. Sadly that didn't remove the FTE penalties from my score. Beware...blowback AR's require a spring that has guns don't!.